As always, I'm curious how anyone would know their oil consumption this accurately, I quote, "In 6000 miles my R1100 oilhead would use about 300cc of 20-50 synthetic oil." 300cc would be aproximatley half the height in the oil level view window.
I agree that an Oilhead with miles on it above 20,000 will certainly stabilize oil use.
My 94 RS has high miles on it, yet uses very little oil. I go about 5,000 miles between oil changes and I may add about 1/2 quart, maybe, in that time before the next change. On the Oilhead oil sight glass, the distance from the bottom of the view port to the top, with the bike level on the centerstand is about one pint of oil, or about 473ml, which is also equal to 473 cc. So from the bottom or top of the window to the center dot is 236 to 237cc. Not enough to worry about as that much oil is easily held up in the cooler and oil lines. So its good to monitor the oil level, but don't obsess about it, just ride more.